Python 实用宝典

Question 1

I just finished writing code to make a plot using pylab in Python and now I would like to superimpose a grid of 10×10 onto the scatter plot. How do I do that?

My current code is the following:

x = numpy.arange(0, 1, 0.05)
y = numpy.power(x, 2)

fig = plt.figure()
ax = fig.gca()
ax.set_xticks(numpy.arange(0, 1, 0.1))
ax.set_yticks(numpy.arange(0, 1., 0.1))
plt.scatter(x, y)
plt.show()

And its output is:

What I would like is the following output:

EDIT: Added an exemple, based on Andrey Sobolev’s answer

Question 2

You want to use pyplot.grid:

x = numpy.arange(0, 1, 0.05)
y = numpy.power(x, 2)

fig = plt.figure()
ax = fig.gca()
ax.set_xticks(numpy.arange(0, 1, 0.1))
ax.set_yticks(numpy.arange(0, 1., 0.1))
plt.scatter(x, y)
plt.grid()
plt.show()

ax.xaxis.grid and ax.yaxis.grid can control grid lines properties.

Question 3

To show a grid line on every tick, add

plt.grid(True)

For example:

import matplotlib.pyplot as plt

points = [
    (0, 10),
    (10, 20),
    (20, 40),
    (60, 100),
]

x = list(map(lambda x: x[0], points))
y = list(map(lambda x: x[1], points))

plt.scatter(x, y)
plt.grid(True)

plt.show()

In addition, you might want to customize the styling (e.g. solid line instead of dashed line), add:

plt.rc('grid', linestyle="-", color='black')

For example:

import matplotlib.pyplot as plt

points = [
    (0, 10),
    (10, 20),
    (20, 40),
    (60, 100),
]

x = list(map(lambda x: x[0], points))
y = list(map(lambda x: x[1], points))

plt.rc('grid', linestyle="-", color='black')
plt.scatter(x, y)
plt.grid(True)

plt.show()

Question 4

Using rcParams you can show grid very easily as follows

plt.rcParams['axes.facecolor'] = 'white'
plt.rcParams['axes.edgecolor'] = 'white'
plt.rcParams['axes.grid'] = True
plt.rcParams['grid.alpha'] = 1
plt.rcParams['grid.color'] = "#cccccc"

If grid is not showing even after changing these parameters then use

plt.grid(True)

before calling

plt.show()

Question 5

The pylab examples page is a very useful source. The example relevant for your question:

http://matplotlib.sourceforge.net/mpl_examples/pylab_examples/scatter_demo2.py http://matplotlib.sourceforge.net/users/screenshots.html#scatter-demo

Question 6

Here is a small example how to add a matplotlib grid in Gtk3 with Python 2 (not working in Python 3):

#!/usr/bin/env python
#-*- coding: utf-8 -*-

import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk
from matplotlib.figure import Figure
from matplotlib.backends.backend_gtk3agg import FigureCanvasGTK3Agg as FigureCanvas

win = Gtk.Window()
win.connect("delete-event", Gtk.main_quit)
win.set_title("Embedding in GTK3")

f = Figure(figsize=(1, 1), dpi=100)
ax = f.add_subplot(111)
ax.grid()

canvas = FigureCanvas(f)
canvas.set_size_request(400, 400)
win.add(canvas)

win.show_all()
Gtk.main()

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